Linezolid is a synthetic antibiotic, the first of the oxazolidinone class, used for the treatment of infections caused by multi-resistant bacteria including streptococcus and methicillin-resistant Staphylococcus aureus (MRSA). The antibacterial effect of oxazolidinones is by working as protein synthesis inhibitors targeting an early step involving the binding of N-formylmethionyl-t-RNA to the ribosome.
Linezolid is marketed by Pfizer under the trade name “Zyvox” and it is chemically known as (S)—N-[[3-(3-fluoro-4-morpholinylphenyl)-2-oxo-5-oxazolidinyl] methyl] acetamide having the formula (I).

Linezolid is first disclosed in U.S. Pat. No. 5,688,792 and its process comprises the use of R-glycidylbutyrate which results in the formation of (R)—N-[[3-[3-fluoro-4-morpholinyl] phenyl]-2-oxo-5-oxazolidinyl] methanol which in the subsequent stages has to be converted to various intermediary compounds to finally form Linezolid. Said process, which is depicted in the scheme-I given below, also encompasses an intermediary azide compound, which is difficult to handle at industrial level:

WO 1999/24393 A1 discloses a process for the preparation of oxazolidinone derivatives, which is depicted in scheme-II given below:
where Roxa is phenyl substituted with one fluoro and one substituted amino group, wherein the substituted amino groups include 4-(benzyloxycarbonyl)-1-piperazinyl, 4-morpholinyl and 4-hydroxyacetylpiperazinylX1 is C1-C20 alkyl;X2 is CI, BrRN is C1-C5 alkyl# indicates that the atoms marked with a (#) are bonded to each other resulting in the formation of ringand RING is

However, WO' 393 does not disclose any specific examples or suitable conditions for the preparation of Linezolid.
WO 2005/099353 A2 discloses a process for the preparation of Linezolid, which is depicted in scheme-III given below:

WO 2006/008754 A1 discloses a process for the preparation of Linezolid, which is depicted in scheme-IV given below

WO2007116284 discloses a process for preparing Linezolid, which is depicted in the scheme-V below, by reacting a compound of structure (1) with a compound of structure (2) at a temperature range from ambient temperature to about 65° C. to provide a compound of structure (3), which is hydrolyzed and subsequently acylated to give Linezolid:

The disadvantages of this process is that it involves an additional reaction for the preparation of the compound of structure (1). Schiff s bases are sensitive to water, so that it may not lead to a formation of pure compound (1), which enhances impurity and byproducts formation.
(S)-Glycidyl phthalimide known as 2-[(2S)-Oxiran-2-ylmethyl]-1H-isoindole-1,3(2H)-dione of formula (IX) is a key intermediate used in all synthetic routes of Linezolid.
2-[(2)-Oxiran-2-ylmethyl]-1H-isoindole-1,3(2H)-dione (I) was first mentioned in Compt. rend. 1930, 190, 495-6, which describes a process for the preparation of 2-[(2)-oxiran-2-ylmethyl]-1H-isoindole-1,3(2H)-dione comprising the reaction of potassium phthalimide with epibromohydrin in the presence of gaseous or aqueous hydrohalogen acids. This process is schematically shown below:

U.S. Pat. No. 5,608,110 discloses a process for the preparation of 2-[(2S)-oxiran-2-ylmethyl]-1H-isoindole-1,3(2H)-dione (I) comprising the reaction of phthalimide with (S)-(+)-epichlorohydrin under reflux in ethyl acetate/hexane under a nitrogen atmosphere to get (S)-1-chloro-3-phthalimido-2-propanol which is cyclized in presence of NaH/THF.
The above process is schematically shown below:

U.S. Pat. No. 6,875,875 discloses a process for the preparation of 2-[(2S)-oxiran-2-ylmethyl]-1H-isoindole-1,3(2H)-dione (I) comprising the reaction of phthalimide with (S)-epichlorohydrin in the presence of an alkali metal carbonate, an alkali metal hydrogen carbonate or a quaternary ammonium salt to get (S)-1-chloro-3-phthalimido-2-propanol which is cyclized in the presence of metal alkoxides. This process is schematically shown as below:

Probably due to the fact that the processes for the synthesis of (S)-glycidyl phthalimide described in U.S. Pat. No. 5,608,110 and U.S. Pat. No. 6,875,875 are carried out under reflux and require high temperatures, the abovementioned approaches yield low optical purities. Ultimately, this issue of the prior art processes results in products (linezolid) with reduced optical purity, and the required purification in order to obtain the desired pure product (such as silica gel column chromatography) is complicated, their industrial application it is difficult and generates a large amount of waste. These problem are in particular addressed by the present invention.
Hence, the use of gaseous or aqueous hydro halogen acids or alkali metal carbonates, alkali metal hydrogen carbonate or a quaternary ammonium salt may not feasible and not economical for industrial production in the preparation of (S)-glycidyl phthalimide.
In their search of an eco-friendly, industrial feasible process for preparing (S)-glycidyl phthalimide our inventors surprisingly came across the benefits of using primary or secondary amines in the condensation reaction. None of the above prior-art processes teaches or suggests the use of primary or secondary organic bases for the preparation of (S)-glycidyl phthalimide
There is consequently a need for an alternative method for the preparation of Linezolid and its intermediates, which does not involve the problems described above. Therefore, there is a need in the art for a simple and facile process for the synthesis of Linezolid, and our inventors have developed a cost-effective and industrially viable process.